Electrolytic pk-ocess for making stencils



R. H. HARRISON.

ELECTROLYTIC PROCESS FOR MAKING ST ENCILS.

' APPLICATION FILED SEPT. 11. 1 918.-

F .2; M 1;. W 5.

l/VI/ENTOR TTOR/VE VS Patented July 29, 1919.

' positin RALPH H. HARRISON, DETROIT, MICHIGAN.

ELECTROLYTIC PROCESS FOR NG STENCILS.

Specification of Letters Patent.

Patented July 29, 1919.

Application filed September 11, 1918. Serial No. 253,614.

To all whom it may concern:

Beit known that I, RALPH H. HARRISON, a citizen of the United States, and residing at Detroit, in the county of Wayne and .areas of the plate and so connecting these areas with wires or strips of such fineness that when paint, ink or pigment is applied to the stencil the interruption offered by the wires or strips to the passage of the coloring matter is negligible. It further consists in dea thin reticulated film of metal upon t 'e tonal areas of a photographic negative plate and upon narrow connections integral with the tonal areas so that none of the areas when thus covered with the metal vwill be disconnected from the remainder,

then coating the treated surface of the plate wlth chromatized gelatin, then rendering the gelatin between the tonal areas and connectors insoluble in water, then removing the portions of the gelatin immediately above the metal covered tonal areas and connectors, and then depositing additional metal upon these areas and connectors until a stencil of the-desired thickness is attained. It also consists in protecting the operative top and bottom faces of the stencil-and then reducing the widths of the tonal areas and of the connectors between them longitudinally of the stencil by means of an etching bath in order to enlarge the open spaces of the stencil. It also consists in covering one side and the edges ofthe tonal areasand the connectors between them in such a" manner as to prevent deposit thereon and then electrically depositing on the other side of the stencil such additional thickness of metal or metals as may be desired.

The tonal area of a stencil is here considered as one, irrespective of its size, which will prevent the deposit of paint, ink or pigment, and which will cause the production of a more or less uncolored area. It is the reverse of what 'is usually termed a tonal area in a photograph but is the same as the tonal area of a negative. The stencils which are produced by the present process are substantially negatives and as perfect positive photographs may be printed therefrom on sensitized paper as if these stencils were the negatives on which the stencils were made. he term gelatin hereinafter employed is intended to embrace glue, soluble gums, al-

bumin and similar vehicles which may be impregnated with salts which are sensitive to light, .such as chromates of ammonium and potassium and which will cause t e vehicle to become hard and insoluble in water where exposed to light.

In the accompanying drawing, Figure 1 is a diagrammatic section of a finished photographic plate adapted for the present process. F 1g. 2 is a similar section after a metal has been electro-chemically deposited thereon. Fig. 3 is a similar section after a layer of chromatized gelatin has been spread over the electro-chemically deposited metal. Fig. 4 is a .similar section after the gelatin has been exposed to light and the unaffected gelatin removed. Fig. 5 is a similar section showing the stencil brought up to the desired thickness by electro-plating. Fig. 6 is a similar section showing a layer of acid resistant material deposited on the top of the previously deposited metal. Fig. 7 is a similar section showing the metal on the glass plate after the gelatin has been removed and the metal has been subjected to the action of an etching medium to increase the spaces between the parts of the stencil. Fig. 8 is a similar section showing the stencil after the projecting edges of the protecting material have been removed. Fig. 9 is a similar section of the stencil after it has been treated with a plastic material to permit the stencil being strengthened. Fig. 10 is a plan of a small section of a stencil.

Similar reference characters refer to like parts throughout the several views.

A temporary supporting medium such as a sheet of glass 1 of pro er size for the stencil is coated with a su stratum such as a solution of rubber or an albumin which may be later on impregnated with a salt which is sensitive to light and will render this substratum acid resistant. Collodion is now flowed over the albumin in the usual manner to produce a wet plate and the well known methods of making half-tone negatives followed with the exception that all the tonal areas of the negative must be connected for otherwise parts of the stencil would fall away. This negative forms the basis for the finished stencil and all the dark areas of the negative will be reproduced in the stencil as areas of metal which will cover and protect portions of the object to be stenciled.

Before the negative is dried the albumin substratum is impregnated with ammonium bichromate or other suitable salt which is sensitive to light. When the plate is dry, the glass side is exposed to light which will render the albumin acid resistant. The albumin may be impregnated with the bichromate before it is applied and then dried on the support after which it is dried, exposed and washed, after which the collodion is applied. -If a rubber substratum is used this treatment is unnecessary.

While the connecting lines are preferably evenly spaced and in two sets at right angles to each other, any other scheme may be employed so long as the lines in the negative are not separated anywhere more than the diameter of an of the tonal areas to .be hereinafter descri ed. The plate after this double exposure, either of which may be first, (or they may be simultaneous) is then finished in the ordinary mannerand the coating thereon will be found'to consist of minute dots and larger areas 2 connected to each other by fine lines 3.

The sensitized plate is given double exposure, one to obtain a negative of the picture or device to be reproduced by the stencil'and the other to obtain a network of finelines which will connect the tonal areas of the negative. This may be done by using an ordinary engravers screen or by photographing a net work of any desired character.

The next step is to make these areas and lines better electric conductors so that heavy. metal may be electrically deposited thereon. This may be done in any rglesired manner but preferably by flooding-the coated side of the plate with a solution of'oopper salt in which fine metal fillings are suspended. Copper nitrate and iron fillings are preferred. Metallic copper is deposited in the form of lines 4 and areas 5 which are good conductors, and all are connected to constitute a reticulated film of copper. A circuit wire may be attached to one edge of the plate and it may be placed in an electrotypers bath and built up with copper so that it will not easily become scratched.

It is well known that when metal is de-' posited on two wires quite near each other that the distance between these wires will rapidly diminish during the deposit.

This would also occur if the plate with the copper faced dots and wires were in position to receive such a deposit, in fact, in a few minutes, the plate shown in Fig. 2 would be covered with an unbroken film of metal electrically deposited thereon. To prevent this, this plate is covered. with a thin layer 7 of chromatized gelatin, that is, gelatin havmg an admlxture of ammonium or potassium chromate. The gelatin may be gum, glue or other suitable material. The bare side of the glass plate is now exposed to a bright light which hardens the gelatin between the areas and lines and renders it insoluble in water.

The gelatin above the opaque areas and lines being protected from the light remains soluble and is washed away. The gelatin between the areas and lines absorbs water and swells so as to form small ridges 8 projecting up above the upper surfaces of the copper faced areas and lines.

The plate is now connected to the negative, pole in an electrotypers bath and a metal, preferably copper, is deposited on the areas and lines between the ridges or projections 8 of gelatin until a sufiicient thickness is attained. The gelatin may now be removed by caustic soda and the reticulated sheet of metal removed from the gla plate and is now ready to be used as a stencil. The.

stenciling may be done in any desired mani'ier but is preferably accomplished by placing the stencil on the surface that is to receive the imprint and then blowing a spray of paint or ink against the stencil by means of an air brush.

While any number may be employed there are preferably from one hundred to two hundred connecting strips per lineal inch connecting the tonal dots or areas 9 and these strips 11 are so fine that when the ink reaches the object to be decorated it will pass under these narrow strips and form a confrom a few ten thousandths to a few hundredths of an inch in thickness although greater thickness may be desired under unusual conditions.

If any portion or all of the stencil is to be 11W tinuous flat color. The stencils may vary a thus reducing their widths. Afterthe action of the acid has been stop )ed the over.- hanging edges of the coating w iich has been protecting the tops of the connectors and areas are brushed of. v

If the stencil 13 is found to be too thin it may be coated on one side with refined tar, beeswax, parafiin or other plastic material 14 which is not affected by the plating bath and this plastic material may be forced into and through the-openings in the stencil to such an extent that it extends up out of the holes in the stencil a greater distance than the desired increase in thickness of the stencil.

The stencil with the adherent plastic material is then suspended in the plating bath and the prisms 15 of plastic material which extend up through the holes in the stencil will prevent the newly deposited metal from extending laterally beyond the edges of the tonal areas and the connecting strips.

A mask may be applied to any portion of the original negative by painting the finished plate before the first deposit of metal with a solution of gun albumin or other gelatin impregnated with an electric conductor such as silver sulfid and a substance sensitive to light such as ammonium bichromate. The remainder of the negative is then covered with a chromatized gelatin as before stated and the plate is exposed to the lightto fix the unexposed gelatin.

When silver is deposited on a thin copper stencil and the two metals are heated to the melting point of silver, the two metals will amalgamate and a very tough sheet is produced. It is always desirable to anneal copper stencils before using them. While in practice the metal strips which connect the tonalareas of the stencils are usually deeper than they are wide, this is not always necessary. When properly made, stencils of this character will print landscapes and pictures of interiors with all the complete details which are shown by photographs. f

Reproductions in two'or more colors may be made by making a stencil for each color through a photo-engravers half-tone or other screen and all colors are printed one above the other to form a composite whole.

It is to be understood that the connecting strips of the reticulated sheet or stencil may be provided for by drawing" lines or other connectors directly onto the picture, drawing or other object which is to be reproduced. Where the object or picture or design to be reproduced is already provided with suitable lines, additional lines or an additional exposure to provide these lines will not be necessary.

1. The process of forming a metallic stencil which consists in iving a sensitive photographic plate a dou%le exposure, one

to obtain a negative of the picture or device to be reproduced and the other to obtain a network of fine lines which will connect the tonal areas of the negative of the picture, then developing the negative, coating the areas and lilies of the negative with copper, and then electrically depositing metal upon the copper.

2. The process of forming a stencil which consists in depositing a metal on the dark lines and areas of a photographic negative, then filling the spaces between said lines and areas with chromatized gelatin and then depositing more metal on said lines and areas between the areas of gelatin until the desired thickness is obtained.

3. The process of forming a stencil which consists in depositing a metal on the dark lines and areas of a photographic negative while the sensitive film still adheres to the plate on which it was exposed, then coating the'face of the metal opposite the plate with an etching medium resistant material, and then etching away the sides of the lines and areas to enlarge the spaces between them.

4. The process of forming a stencil which the lines and tonal areas of a finished photographic negative plate, in which two intersecting sets of parallel lines connect the areas, until the height of the lines exceeds the distances between them.

5 The process of forming a stencil which consists in depositing a thin film of metal on the tonal areas of a photographicnegative and on lines connecting all the tonal areas, then coating with gelatin impregnated with a light-sensitive salt and exposing the coated negative to light, then removing the gelatin above the areas and lines and then electrically depositing more metal on the tonal areas and connecting lines until the desired thickness is obtained.

f6. The process of forming a metal stencil which consists in photographically exposing a sensitized plate to the 0b ect to be pictured and to a grating, then finishing the negative, then depositing a thin film of copper consists in electrically depositing copper on upon .the tonal areas and the lines on the I negative, then applying means to the plate to restrict laterally the deposit of the metal and then completing the deposit of the metal necessary to form the stencil.

7. The process of forming a metallic stencil which consists in producing on a sen sitive plate by photographic means a negative of the picture -or design to be. reproduced and fine lines connecting all the tonal areas of the negative of the picture or design, then developing the negative, coating the areas and lines ofthe negative with an electric conductive metal, filling the spaces between the lines and areas with a non-conducting material, and then electrically de-' positing more metal on'the lines and areas.

8. The process of forming a metallic stencil which consists in so exposing a sensitive 5 photographic plate as to-.fi obta'in a ne ative comprising the pictiire or design to reproduced together with fine lines which connect the tonal areas of the picture or design, then developing the negative, coating the areas'and lines of the negative with an electric conductive material, and then depositing metal on the said conductive material.

RALPH H. 11301. 

